1. Field of the Invention
This invention relates to the configuration of a plasma display panel and a drive method for a plasma display panel.
2. Description of the Related Art
Nowadays, as thin-screen display devices, plasma display panels (hereinbelow, abbreviated to the “PDPs”) of AC type (AC discharge type) have been put into commercial production. In the PDP, two substrates, namely, a front transparent substrate and a rear substrate, are arranged in opposition through a predetermined spacing. A plurality of row electrode pairs in which row electrodes forming the respective pairs extend in the lateral direction of a screen are formed on that inner surface of the front transparent substrate (a surface opposing to the rear substrate) which is a display surface. Further, a dielectric layer which covers the respective row electrode pairs are formed on such an inner surface of the front transparent substrate. On the other hand, a plurality of column electrodes which extend in the vertical direction of the screen so as to intersect the row electrode pairs are formed on the rear substrate. In a case where the PDP is viewed from the side of the display surface, pixel cells corresponding to pixels are formed at the intersection parts between the row electrode pairs and the column electrodes.
In a prior-art AC type plasma display panel (“PDP”) of surface discharge scheme, a magnesium oxide layer which contains magnesium oxide crystals that have the characteristic of presenting cathode-luminescence emission (hereinbelow, termed the “CL emission”) having a peak within a wavelength region of 200-300 nm, by excitation based on an electron beam, is formed as a protective layer on the surface of a dielectric layer covering row electrodes as confront discharge cells, whereby discharge characteristics such as the discharge delay time of a discharge generated within the discharge cell are improved by the characteristic of the magnesium oxide crystals contained in the magnesium oxide layer. For example, Japanese Patent Kokai No. 2006-59779 (Patent Document 1) discloses the above-described PDP.
Besides, in a prior-art PDP, a magnesium oxide layer which contains magnesium oxide crystals that present photoluminescence emission (hereinbelow, termed the “PL emission”) radiating ultraviolet radiation with a peak wavelength at 230-250 nm, when excited by ultraviolet radiation radiated from a discharge gas, is formed at, at least, a part confronting each discharge cell, between a front substrate and a rear substrate, and a fluorophor layer fluoresces when excited by the ultraviolet radiation which is radiated by the PL emission of the magnesium oxide crystals contained in the magnesium oxide layer, and the ultraviolet radiation which is radiated from the discharge gas, whereby an intensity can be enhanced. For example, Japanese Patent Kokai No. 2006-59786 (Patent Document 2) discloses the PDP mentioned above.
Further betterments in the discharge characteristics and further enhancement in the intensity are required of such prior-art PDPs. It is also required to prevent the lowering of a dark contrast attributed to reset discharges (discharges for initializing all the discharge cells) which are performed within the discharge cells during the drive of the PDP.
Such a PDP is subjected to a gradation drive employing a subfield method, in order to obtain a display intensity of halftone corresponding to an input video signal.
In the gradation drive based on the subfield method, a display drive for the video signal for one field is performed in a plurality of subfields to which the numbers of times (or periods) for performing light emissions are respectively allotted. In each subfield, an address step and a sustain step are successively executed. In the address step, selective discharges are caused between the row electrodes and the column electrodes within the respective pixel cells in accordance with the input video signal, thereby to form (or erase) predetermined quantities of wall charges. In the sustain step, only the pixel cells formed with the predetermined quantities of wall charges are repeatedly discharged, thereby to sustain light emission states induced by the discharges. Further, in at least the head subfield, a reset step is executed in advance of the address step. In such a reset step, the reset discharges are caused between the paired row electrodes within all the pixel cells, thereby to initialize the quantities of the wall charges remaining within all the pixel cells.
Here, the reset discharges are comparatively strong discharges and are not pertinent to the contents of an image to-be-displayed at all. Therefore, the PDPs have had the problem that the light emissions induced by the discharges lower the contrast of the image.
In this regard, there have been proposed a PDP and a drive method therefor wherein magnesium oxide crystals which present cathode-luminescence emission having a wavelength peak within 200-300 nm, when excited by electron beam irradiation, are stuck on the surface of a dielectric layer covering row electrode pairs, thereby to shorten a discharge delay time. For example, Japanese Patent Kokai No. 2006-54160 (Patent Document 3) discloses this PDP. According to such a PDP, a priming effect after a discharge continues for a comparatively long time, and hence, a weak discharge can be caused stably. Therefore, a reset pulse in a pulse waveform whose voltage value arrives at a peak voltage value gradually with the lapse of time is impressed on the row electrodes of the PDP as stated above, whereby a weak reset discharge is caused between the row electrodes adjacent to each other. Owing to the weak reset discharge, a light emission intensity attendant upon the discharge becomes low, so that the contrast of the image can be heightened.
Even with such a drive method, however, the so-called “dark contrast” in the case of displaying a dark image cannot be satisfactorily heightened, and this has posed the problem that the dark image cannot be offered in a state of high quality.